Labyrinthodon /rom Warwickshire. 527 



uninterruptedly confluent, and form a single broad and strong piece of bone, sup- 

 porting the dentary piece upon a groove along its upper surface (fig. 2, h.), and ter- 

 minating anteriorly at the bend of the expanded dentary element, which there re- 

 ceives the extremity of the angular element in a notch. 



The fossil fragment exhibiting the above structure is five inches and a half in 

 length, and probably forms little more than the anterior third of the ramus of the 

 jaw ; there is sufficient, however, to demonstrate that its structure is essentially 

 Batrachian. A similar portion of the lower jaw of a Saurian would have exhibited 

 either the dentary element simply, or inclosed at the posterior fractured end, be- 

 tween the extremities only of the separate angular and opercular elements. The 

 continuation of the angular element alone, forming the lower half of the ramus, to 

 near the symphysis, and supporting the dentary piece in a groove on its upper 

 surface, is as striking a Batrachian character in the fossil of the British sandstone 

 as that observed by Prof. Jaeger in the occipital bone of the great Salamandro'ides 

 of the German Keuper. 



The smaller serial teeth in the present portion of jaw are about forty in number, 

 and their sockets are in close contact with each other ; they very gradually diminish 

 in size as they approach both ends of the series, but chiefly so towards the anterior 

 part of the jaw. One of the smallest teeth at this end of the jaw is recumbent in 

 front of the great laniaries ; I think it very probable that it was an incompletely de- 

 veloped tooth of replacement, not yet erected and anchylosed to the bone, — a cir- 

 cumstance in accordance with the view which I have entertained of the place of 

 development of the successional teeth. The alternate sockets are empty in a con- 

 siderable portion of the posterior part of the series, agreeably with the law of shed- 

 ding and replacement illustrated in the Lah. leptognathus, so that the teeth thus 

 appear to be separated by wider intervals than their sockets prove them to be. The 

 form of the teeth is conical, with the base slightly compressed in the direction of 

 the axis of the jaw ; the largest transverse diameter of one of the posterior of these 

 serial teeth, where it emerges from the socket, is three lines ; the same diameter of 

 the anterior serial tooth is one line and a half, its length four lines and a half. The 

 great laniary teeth appear to be three in number in each symphysis, and the one 

 nearest the symphysis is somewhat larger than the other ; but they are probably not 

 in place and use at the same time. The greatest diameter of the base of the largest of 

 these tusks, which is subcompressed, is five lines ; its length, judging from an entire 

 tooth of the same species, must have been at least one inch and a half. The lines 

 of the inflected csementum form well-marked longitudinal striae all around the basal 

 half of the tooth, and the interspaces of the strise form convex ridges, as in the large 

 tooth of which I described the labyrinthic structure in my previous paper, and which 

 is most probably a laniary tooth of the present species. These ridges are fewest near 

 the termination of the striae, being divided and multiplied by new longitudinal striae, 



3y2 



